Definition

1. Noun:
   • A very long period of time; an indefinite, extended duration. This meaning is primarily used in the idiomatic phrase "once in a blue moon."
   • A rare or unusual event. Refers to something that occurs very infrequently.

Usage

The term "blue moon" is almost exclusively used in the fixed idiomatic expression "once in a blue moon." This phrase functions as an adverbial phrase to describe the extreme rarity of an event.

Examples

• Noun (in idiom):
  • My sister lives abroad, so I only see her once in a blue moon.
  • He's very careful with his money and eats at a restaurant only once in a blue moon.
  • Such a total eclipse of the sun happens only once in a blue moon.

Advanced Usage

• "a blue moon": Can be used poetically or figuratively to mean a very rare occurrence, though this is less common than the full idiom.
  • Opportunities like this come along only a blue moon.

Variants and Related Words

• Blue moon: In modern astronomy, a "blue moon" can refer to the second full moon in a single calendar month, which is the origin of the idiom's meaning of rarity. This is a separate, technical definition.
• Rarity (n): The state or quality of being rare.
• Infrequency (n): The state of not happening often.

Synonyms

• Rarely
• Seldom
• Hardly ever
• Infrequently

Related Idioms

• Once in a blue moon: Very rarely; almost never.
  • He visits his hometown once in a blue moon.
• Every blue moon: An occasional variant with the same meaning as "once in a blue moon."
  • We get a chance to relax like this every blue moon.

Noun

1. a long time
   • something that happens once in blue moon almost never happens